The forgotten methane source

Jan 11, 2006

A plant chamber used to investigate methane formation in plants -- in this example, in ryegrass (Lolium perenne). Image: Max Planck Institute for Nuclear Physics.

In the last few years, more and more research has focused on the biosphere; particularly, on how gases which influence the climate are exchanged between the biosphere and atmosphere. Researchers from the Max Planck Institute for Nuclear Physics have now carefully analysed which organic gases are emitted from plants. They made the surprising discovery that plants release methane, a greenhouse gas - and this goes against all previous assumptions.

Equally surprising was that methane formation is not hindered by the presence of oxygen. This discovery is important not just for plant researchers but also for understanding the connection between global warming and increased greenhouse gas production (Nature, January 12, 2006).

Methane is the greenhouse gas which has the second greatest effect on climate, after carbon dioxide. The concentration of methane in the atmosphere has almost tripled in the last 150 years. Methane is best known as natural gas, currently an important energy source. Nonetheless, only part of the methane uptake in the atmosphere is due to industrial activities connected to energy production and use. More important for the increase of methane in the atmosphere is the increase in so-called "biogenic" sources, e.g., rice cultivation or domestic ruminants related to the rise in the world's population. Nowadays, methane in the atmosphere in fact is largely of biogenic origin.

Until now, it has been assumed that biogenic methane is formed anaerobically, that is, via micro-organisms and in the absence of oxygen. In this way, acetate or hydrogen and carbon dioxide are transformed into methane; they themselves are created in the anaerobic decomposition of organic materials. The largest anoxic sources of methane are wetlands and rice fields, as well as the digestion of ruminants and termites, waste disposal sites, and the gas produced by sewage treatment plants. According to previous estimates, these sources make up two-thirds of the 600 million tonnes worldwide annual methane production.

Scientists from the Max Planck Institute for Nuclear Physics have now discovered that plants themselves produce methane and emit it into the atmosphere, even in completely normal, oxygen-rich surroundings. The researchers made the surprising discovery during an investigation of which gases are emitted by dead and fresh leaves. Then, in the laboratory and in the wild, the scientists looked at the release of gases from living plants like maize and ryegrass. In this investigation, it turned out that living plants let out some 10 to 1000 times more methane than dead plant material. The researchers then were able to show that the rate of methane production grew drastically when the plants were exposed to the sun.

Although the scientists have some first indications, it is still unclear what processes are responsible for the formation of methane in plants. The researchers from Heidelberg assume that there is an unknown, hidden reaction mechanism, which current knowledge about plants cannot explain - in other words, a new area of research for biochemistry and plant physiology.

In terms of total amount of production worldwide, the scientists' first guesses are between 60 and 240 million tonnes of methane per year. That means that about 10 to 30 percent of present annual methane production comes from plants. The largest portion of that - about two-thirds - originates from tropical areas, because that is where the most biomass is located. The evidence of direct methane emissions from plants also explains the unexpectedly high methane concentrations over tropical forests, measured only recently via satellite by a research group from the University of Heidelberg.

But why would such a seemingly obvious discovery only come about now, 20 years after hundreds of scientists around the globe started investigating the global methane cycle? "Methane could not really be created that way," says Dr. Frank Keppler. "Until now all the textbooks have said that biogenic methane can only be produced in the absence of oxygen. For that simple reason, nobody looked closely at this."

The fact is that, in order to determine the quantity of emissions, scientists indeed have to make very careful measurements. The researchers from Heidelberg conducted most of their experiments in methane-free air, in order to factor out the high natural background of methane. Furthermore they used isotope analysis to show beyond doubt that this was an undiscovered process of methane production. By "looking closely" - despite established opinion - they made a discovery that will require textbooks to have their passages about methane production rewritten.

Following up on this discovery, the scientists now will continue laboratory work, as well as field and remote sensing studies, to better quantify the strength of these methane emissions. A related exciting question is which role the biosphere has played in methane production in the history of the earth, and what kind of influence rising global temperatures and carbon dioxide concentration have on the production of methane from plants. Answers to these questions are important for understanding the feedback mechanisms between climate change and greenhouse gas production.

Relevant PhysicsForums posts

Related Stories

President Barack Obama ordered the federal government on Thursday to cut its greenhouse gas emissions by nearly half over the next decade, driving his climate change agenda forward despite percolating challenges ...

The Center for Research and Technological Development in Electrochemistry (CIDETEQ) in Mexico has obtained biogas from "garbage or organic waste", having replaced part of the natural gas used by the Pilgrim's ...

AZTI's Food Research Unit has managed to obtain a series of food prototypes using whey produced by cheese-making dairies, which allows a commercial outlet to be provided for an organic product that is routinely treated as ...

With exploding consumer demand for Greek yogurt, production is up. That's great for food companies' bottom lines, but it also leaves them dealing with a lot more acid whey, a problematic byproduct of the ...

Caltech scientists, inspired by a chemical process found in leaves, have developed an electrically conductive film that could help pave the way for devices capable of harnessing sunlight to split water into ...

Last Wednesday the lecture theatre at the Empa Academy was filled to the very last seat as speakers from the automobile, energy and finance sectors as well as researchers and those involved in the politics of energy presented ...

Recommended for you

Certain specimens of the fossil Dickinsonia are incomplete because ancient currents lifted them from the sea floor, a team of researchers led by paleontologists at the University of California, Riverside has fo ...

Why does time seem to crawl if you're waiting in line at the post office, but hours can fly by in minutes when you're doing something fun? A new study in the Journal of Consumer Research examines the factors that determine how co ...

Why do some consumers make choices based on their feelings instead of rational assessments? According to a new study in the Journal of Consumer Research, consumers who consider themselves independent are more inclined to rel ...

Why is it so hard for consumers to save money? According to a new study in the Journal of Consumer Research, consumers are often impatient and do not think about the long-term consequences of spending money. ...

Does hearing about a company's charitable donations raise your opinion of their products? According to a new study in the Journal of Consumer Research, corporate social responsibility leads consumers to believe products are be ...

User comments : 0

Please sign in to add a comment.
Registration is free, and takes less than a minute.
Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.